In the field of medical technology, considerable use has been made of electrical monitoring equipment such as electrocardiograph (ECG) apparatus. In using ECG equipment it is common practice to attach a plurality of body electrodes to a patient which are engageable by shielded-conductor patient monitoring leads having suitable electrode attachment terminal clips or plugs. The several monitoring leads are connected, through a junction box, to corresponding conductors in a so-called bulk cable, the latter comprising a plurality of shielded-conductor ECG leads, all surrounded by an additional foil-type shield, and being connected back to the ECG equipment. The patient monitoring leads extending from the junction box are subjected to considerable wear, often to the extent of requiring replacement. Depending upon use, a monitoring lead may need replacement every two or three months.
Prior art patient monitoring lead assemblies include junction boxes generally having a plurality of surface-mounted jacks. The leads are individually plugged into these jacks and are readily replaceable in the event of failure or breakage. Many types of jacks are used including phone jacks, coaxial jacks and arrangements in which the mating plug and jack are threaded or otherwise "locked" together. Naturally, the large number of individual jacks and their mounting arrangements tends to complicate the box design.
The individual jacks have generally high reliability, since they are designed for a great number of mating-unmating operations. Such jacks are underutilized in an ECG environment because of the relatively few mating-unmating operations and are not cost-effective. Further, with the exception of the very expensive locked arrangements, it is difficult to provide strain relief for the monitoring leads without increasing the wear-and-tear on the jack and plug assembly. It is thus not unusual to experience high failure rates in the plug and jack assemblies despite the fact that they are designed for more mating-unmating cycles than are encountered in normal ECG use. This has been a continuing problem in the ECG field.
When the nature of the ECG cable assembly and its use is considered the apparent inconsistency between poor field reliability experience and the use of relatively high reliability components may be reconciled. In an ECG environment the patient monitoring leads coming from the junction box are by-and-large unsupported. The leads extend in different directions and tend to tangle quite easily, which subjects them to bending moments and consequent strain on the connections at the junction box. Therefore, it is believed that the prior art use of jack and plug connections in these junction boxes has not been conducive to high reliability.
The present invention is based upon the operational environment of the ECG junction box and departs from the prior art in that it involves removing the connections to a protected area within the junction box itself, incorporating a low cost semi-permanent type of connector device and providing adequate strain relief of the individual monitoring leads away from the connection points. This is achieved with the system of the invention while retaining the desirable features of the prior art. Though the procedure for field replacement of defective patient monitoring leads is more complex (in the preferred embodiment an openable portion or access panel is removable to allow access to the interior of the junction box), the resultant saving in wear-and-tear on patient monitoring leads and connection points and the improved reliability is more than sufficient compensation.